Abstract

Some remarks on the geological evolution of the South-Eastern Marsica (Abruzzo, Central Apennines), based on an interdisciplinary analysis of stratigraphic and structural data. This paper presents an interdisciplinary approach to the understanding of the geological evolution of the south-eastern Marsica (Abruzzo), in the central-southern Apennines of Italy (fig. 1). A detailed geological survey (1:10.000) (fig. 2) and an analysis of the sedimentary facies have permitted the present tectonic setting of the area to be described and some aspects of the original position of the different palaegeographic domains to be explained. We identified two stratigraphic successions (fig. 3): an edge-fore reef platform sequence located in the western sector (Mt. Marsicano and Serra dei Balzi) and a clastic and lacunose slope sequence in the eastern and southern sectors (Mt. Mattone and Mt. Amaro). The tectonic evolution of the area is connected with a Mio-Pliocene compressional phase, with north-eastern vergence, overprinted by a Plio-Quaternary extensional phase (Miccadei, 1993; Corrado et alii, 1990). The compressive structure consists of the in-sequence eastward stacking of four carbonatic fold-and-thrust tectonic units (Mt. Amaro-Mt. Sterpi d'Alto, Mt. Marsicano, Serra dei Balzi, Mt. Mattone) overthrust on to pre-evaporitic siliciclastic units of early Messinian age. In some cases, the contacts between the tectonic units mark transitions between different palaeogeographic domains, suggesting a possible re-activation of the pre-orogenic Mesozoic basin structures. The facies transition along an E-W section across the structures of M. Marsicano, Mt. Mattone and Mt. Greco allows the different stratigraphic units to be ascribed to a depositional system, that records a general eastward transition from edge to basin. Therefore, the present relative position of the tectonic units reflects their original positions. In particular, the Mt. Mattone structure played an important role since Jurassic times; it was a structural high, located between Montagna Grande and Mt. Genzana, that controlled the dispersion pattern of materials coming from the edge and feeding the deposition of breccias and megabreccias. The principal extensional structure of the area is the M. Marsicano-Val di Sangro fault system. It consists of three segments (fig. 5) with different orientation and kinematics. The northern segment (A-B in fig. 5), which dips SW at about 70 degrees , has undoubted normal kinematics; the central segment, which dips WSW at about 75 degrees , also has normal kinematics; the southern segment, which dips southward at about 80 degrees , has normal-right lateral oblique kinematics. Field evidence suggests that the latter two segments may represent the reactivation of a left-lateral strike-slip discontinuity of the Mio-Pliocene compressional phase. In conclusion, the stratigraphic and structural data together with the construction of geological sections show that the present tectonic setting of the area is the result of a long geological history during which pre-existing structures, inherited both from the Mesozoic rifted continental margins and from the Miocene compressional phase, were often reactivated and inverted.

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